1. Field of the Invention
The present invention relates in general to a secure, wireless communication system utilizing synchronized noise signals for coding and decoding message signals and, more particularly, to a communication system in which the noise signals are locally synchronized on a substantially continuous basis to assure accurate and reliable transmission of information between transceiver units of the system.
2. Description of the Prior Art
In the art of secure communications, particularly in systems which use a plurality of transceiver units wirelessly linked to one another, it is known to use signals having the same predetermined known pattern to both encode and decode the message signal at the transmitting and receiving transceivers. Although the encoding and decoding signals have specific known patterns, they are referred to as noise signals since they appear, in the absence of the required decoding key, to be noise. For proper operation, the noise generating circuits of the respective transceiver units must be synchronized with each other such that the noise signal used to encode a message signal within one transceiver before transmission can be readily stripped within another transceiver after reception. Many of these known systems require transmission of initialization or reset pulses to each transceiver unit in order to synchronize the encoding and decoding noise signals, i.e. the reset pulses must be modulated, amplified and coverted to the proper form for wireless transmission. To be received, the transmitted pulses must be collected by an antenna and thereafter detected or demodulated and amplified. During operation, the encoding and decoding noise signals in the various transceivers of the communication system may lose their synchronization due to drift or other factors. Typically, prior art communication systems will continue with the noise encoding of the message signal during the time that the encoding and decoding noise signals are not in synchronism. As a result, the noise signal cannot be properly stripped by the receiving transceiver, and the message signal may be garbled or lost entirely. Reset pulses may be transmitted on a periodic basis during operation to minimize the period during which synchronization can be lost. If, however, there is even a slight error in the transmission or reception of the reset pulses, resynchronization will not be attained, and the system will continue to operate with the respective noise generators out of synchronism with one another. As a consequence, the message signal will be unintelligible at the receiving transceiver and the communication system will not provide an acceptable level of reliability.